This invention relates to a method of providing a substrate with a patterned metal layer disposed thereon, which method has particular application in magnetic bubble domain technology in providing a bubble propagation path of magnetically soft material, such as permalloy on a magnetic bubble-supporting film.
Photolithography techniques as applied to the manufacture of microminiaturized electronic circuit components are well known in the art. A layer of photoresist material sensitive to light, which generally comprises an organic polymer is deposited onto a substrate. The substrate typically may be a semiconductor wafer on which it is desired to form a patterned layer of material which may be either metal or non-metal. In a particular environment, overlay patterns of magnetically soft material (e.g. permalloy) are deposited on a magnetic bubble-supporting film for the purpose of forming bubble propagation paths along which magnetic bubble domains may be moved in response to changes in orientation of a rotary magnetic field in the plane of the magnetic bubble-supporting film. As the in-plane magnetic field is reoriented by the rotation thereof, magnetic poles generated by the bubble propagation path of magnetically soft material are moved, thereby causing movement of the magnetic bubble domains which are attracted by these magnetic poles.
Heretofore, the patterning of such bubble propagation paths from a layer of magnetically soft material applied to a magnetic bubble-supporting film has been accomplished by standard photolithography procedures employing the deposit of photorsist films onto the substrate containing the film of bubble-supporting material and the layer of magnetically soft material to be patterned. The photoresist layer is exposed selectively to electromagnetic radiation, which may include ultra violet light, X-rays, E-beam exposure, wherein the solubility of portions of the photoresist layer is changed. Development of the photoresist layer follows by subjecting same to the action of a solvent material which removes the more soluble portions of the photoresist layer, thereby uncovering parts of the underlying metal layer of magnetically soft material for subsequently etching in forming the desired pattern therein.
The use of ion-milling as an etching technique for subsequently patterning the exposed portions of the layer of magnetically soft material through the patterned photoresist layer has heretofore been generally unsuccessful because the ion milling treatment tended to induce an unsuitably high removal rate of the photoresist layer while also generating sufficient heat in the milling process tending to soften the organic polymer material comprising the photoresist layer.
Additionally, where the photoresist layer itself forms the patterned mask for the underlying layer of magnetically soft material, generally the thickness of the photoresist layer has been of sufficient magnitude to put a restrictive limit on the resolution quality obtainable therefrom in the resulting patterned bubble propagation path of magnetically soft material. In such instance, the increasing emphasis on smaller and smaller geometries for bubble propagation path patterns necessary to accommodate the use of bubbles having diameter sizes of 0.50 microns or lower requires extremely high resolution in transferring the pattern from the developed photoresist layer to the underlying layer of magnetically soft material. Moreover, the photoresist material tends to break down at the edges of the pattern-forming openings therein during the etching procedure as practiced on the exposed regions of the underlying layer of magnetically soft material. This degradation of the edges of the patterned photoresist layer adversely affects the resolution quality of the subsequent pattern obtained in the layer of magnetically soft material following the treatment of the selected regions thereof exposed through the openings in the patterned photoresist layer.